包含/合并问题的实体框架

Question

I've implemented an Table Inheritance functionality demonstrated at http://www.sqlteam.com/article/implementing-table-inheritance-in-sql-server .

All the foreign keys and constraints are in place.

Now I am using Entity Framework to pull back my People, Students, Teachers, and Parents where the model looks something like the following (without all the EF specific attributes etc).

public partial class People : EntityObject
{
  public guid PeopleID { get; set; }
  public int Age { get; set; }  /Added for an example query
  public PeopleParent Parent { get; set; }
  public PeopleStudent Student { get; set; }
  public PeopleTeacher Teacher { get; set; }
}

Now I need to get all People regardless of type, who are 25 years old, no more than 100 records, and I want to include all the referenced data. I create my EF Query like:

IQueryable<People> query = Entities.People.Include("PeopleParent")
                                           .Include("PeopleStudent")
                                           .Include("PeopleTeacher");

query.Where(x => x.Age == 25)
     .Take(100);

IEnumerable<People> results = query.ToList();

Seems simple enough, but whatever table/entityset I've set to include first creates an INNER JOIN instead of the LEFT OUTER JOIN , which is not producing the right results.

Generated TSQL (incorrect for my needs):

SELECT 
  [Limit1].[C1] AS [C1],
  <A bunch of Limit1 Columns>
FROM (
  SELECT TOP (100) 
    [Extent1].[PeopleID] AS [PeopleID],
    <A bunch of Extent1 Columns>
    [Extent2].[PeopleID] AS [PeopleID1], 
    <A bunch of Extent2 Columns>
    [Extent3].[PeopleID] AS [PeopleID2], 
    <A bunch of Extent3 Columns>
    [Extent4].[PeopleID] AS [PeopleID3], 
    <A bunch of Extent4 Columns>
    1 AS [C1]
  FROM [rets].[People] AS [Extent1]
  INNER JOIN [rets].[PeopleParent] AS [Extent2] 
    ON [Extent1].[PeopleID] = [Extent2].[PeopleID]
  LEFT OUTER JOIN [rets].[PeopleStudent] AS [Extent3] 
    ON [Extent1].[PeopleID] = [Extent3].[PeopleID]
  LEFT OUTER JOIN [rets].[PeopleTeacher] AS [Extent4] 
    ON [Extent1].[PeopleID] = [Extent4].[PeopleID]
) AS [Limit1]

Why is the first Include used as an INNER JOIN , and is there a soluion to my problem?

** UPDATE 1**

Assuming I use Ladislav Mrnka's Answer , there are two additional requirements due to the significant change in Linq and Lambda querying.

Question: How do I search for specific People which have specific properties?

(All Students with a Grade of "A")

Answer:

context.People.OfType<Student>().Where(s => s.Grade == "A");

Question: How do I search for any People that have a specific property?

(All Students or Teachers who's PrimaryFocus = "Math")

Answer:

List<People> result = new List<People>();
result.AddRange(context.People.OfType<Student>()
                              .Where(x => x.PrimaryFocus == "Math")
                              .ToList());
result.AddRange(context.People.OfType<Teacher>()
                              .Where(x => x.PrimaryFocus == "Math")
                              .ToList());

Answer 1

The obvious solution for you should be using native EF support for inheritance. In your case TPT inheritance . Once you have inheritance you will simply call:

IEnumerable<People> results = Entities.People
                                      .Where(x => x.Age == 25)
                                      .Take(100)
                                      .ToList();

And it will return you instances of Student , Teachers , Parents etc.

In your solution the only advice is check that the relation is optional (1 - 0..1) - . If it is required it will use INNER JOIN . If it is optional and it still uses INNER JOIN it can be some bug or other problem in your model.